The term “encapsulation material” encompasses in the present context in particular any material which can be brought to an envisaged form by means of casting, injection, injection molding or transfer molding. This includes in particular reaction resins such as epoxyresins, acrylic resins and silicone resins. The use of ceramic or vitreous materials is also conceivable.
In the case of conventional surface-mountable optoelectronic components first of all a prehoused device is produced by encapsulating a prefabricated leadframe with a suitable plastics material by injection molding, said plastics material forming a housing body of the device. Said housing body has a depression for example at the top side, into which depression leadframe terminals are introduced from two opposite sides. A semiconductor chip such as an LED chip for example, is adhesively bonded and electrically contact-connected on one of said leadframe terminals. The other leadframe terminal is connected to the semiconductor chip via a bonding wire. A generally transparent potting composition is filled into the depression. This basic form of surface-mountable optoelectronic components is disclosed for example in the article “SIEMENS SMT-TOPLED für die Oberflächenmontage” [“SIEMENS SMT-TOPLED for surface mounting”] by F. Möllmer and G. Waitl, Siemens Components 29 (1991), issue 4, pages 147-149.
In the case of these known surface-mountable designs, a highly directional radiation can be achieved by the sidewalls of the depression being formed in such a way, for example as suitable inclined or curved areas, that they form a reflector for a radiation emitted laterally or rearward from the semiconductor chip, said reflector deflecting said radiation toward the desired radiation direction. Depending on the form of housing or form of reflector, the component may be constructed as a so-called toplooker, i.e. with a main radiating direction perpendicular or at a steep angle with respect to the mounting plane of the component, or as a so-called sidelooker, i.e. with a main radiating direction parallel or at a shallow angle with respect to the mounting plane of the component. Examples of a toplooker and of a sidelooker with the corresponding forms of housing are shown for example in FIG. 2 and FIG. 3, respectively, of EP 0 400 175 A1.
A thermoplastic material or a thermosetting plastic material is usually used for the housing body of the component. In a preferred embodiment, which is used in practice, a polyphthalamide which is filled with glass fibers and colored white with a TiO2 filler is used as plastics material for the housing body.
For the sake of completeness it should also be pointed out that it is additionally known to form such optoelectronic components with additional optical elements in order to improve their radiating characteristics or to adapt them to specific applications. Thus, by way of example, EP 0 400 176 A1 and DE 197 55 734 A1 show surface-mountable optoelectronic components of the type described in the introduction which are respectively provided with an additional optical device on the housing body and/or the potting composition.
It has been found that when using semiconductor chips which emit radiation from the blue spectral range and/or from the ultraviolet spectral range, in particular GaN-based semiconductor chips in which a radiation-emitting active layer has a GaN, InGaN, AlGaN or InGalN material, the radiation efficiency from the component is unexpectedly low.